IBS or IBD – how can the doctor tell?

By Dr Steven Mann MB ChB, FRCP, Consultant Gastroenterologist

If you go to the GP or Hospital specialist with cramps, diarrhoea and bowel frequency problems, how can the Dr distinguish between irritable bowel syndrome (IBS) and something else like inflammatory bowel disease (IBD) i.e. Crohn’s or ulcerative colitis?

This is a scenario faced on a daily basis by clinicians. As there are only a limited number of symptoms generated from the digestive system, there will inevitably be an overlap of symptoms between different conditions.

IBS is common and generates significant health care costs with a tendency to long term symptoms. It tends to peak in the third and fourth decade with a female predominance. It affects 10-15% of the population of Europe and North America. Crohn’s disease and ulcerative colitis affect about 240,000 people in the UK (400 per 100,000). There is a north-south gradient to the incidence of IBD and the incidence is therefore higher in Scotland. Compared to the non-Jewish Caucasian population, IBD occurs more frequently in Ashkenazi Jews. The incidence of Crohn’s disease may be up to 4 times higher in Ashkenazi Jews compared to the non-Jewish Caucasian population.

IBS is thought to be due to a disorder of gut function, typically associated with a number of normal investigations. IBS symptoms follow a bacterial or viral gut infection in 10% of cases. Other triggers include food or stress.

The process by which the clinicians reach a diagnosis rests on taking a thorough history (the enquiry), examination and investigations, such as bloods tests, stool samples, endoscopy assessments and imaging.

Most patients can have the diagnosis of IBS made confidently after eliciting a good history and examination. It is manifest as abdominal pain or discomfort associated with defaecation or a change in bowel habit; it often has additional lower gastrointestinal symptoms including bloating, distension, flatulence, rectal mucus, rectal dissatisfaction, incomplete evacuation, variable frequency and character of stool. Typically the pattern of abdominal pain may be longstanding and intermittent, with previous similar episodes, and associated with relief following defaecation or passage of flatus. It is characteristic of IBS patients that the pain is severe and debilitating in the absence of any abnormal findings. Bloating is common and may be the most bothersome symptom. The bloating typically gets worse during the day, particularly after meals, with the symptom usually improving or disappearing overnight.

IBS patients may also experience non-gut symptoms including fatigue, backache, headache, period problems, irritable bladder and pelvic pain. Chronic fatigue syndrome, fibromyalgia and psychological disorders such as anxiety and depression are also more common in IBS patients.

In contrast, ulcerative colitis typically presents with bloody diarrhoea and cramps. There may be night-time calls to the toilet which shouldn’t happen in IBS. Crohn’s disease patients may have abdominal pain, weight loss and diarrhoea although the symptoms vary according to the segment of the intestines that are affected.

Investigations in IBS are typically normal- bloods, stool and colonoscopy. This contrasts with IBD patients, where blood tests may demonstrate inflammation with raised ESR and CRP levels, stool samples may also suggest active inflammation using a relatively new investigation called faecal calprotectin, and of course the colonoscopy will show an inflamed lining to the inside of the colon with ulcers and red patches of varying severity. Biopsy samples will help determine whether the inflammation is due to Crohn’s or ulcerative colitis. Crohn’s can affect any part of the intestine and may be interspersed with normal segments, whereas colitis is continuous involving the rectum and extending up the colon (large intestine) but not involving the small intestine.

IBS does not produce the destructive inflammation found in IBD, so in many respects it is a less serious condition. It doesn’t result in permanent harm to the intestines, intestinal bleeding, or the harmful complications that may occur with IBD. People with IBS are not at higher risk for colon cancer, nor are they more likely to develop IBD or other gastrointestinal diseases. IBS seldom requires hospitalisation, and treatment does not involve surgery or powerful medications, such as steroids or immunosuppressives. However we shouldn’t underestimate the negative impact that IBS has on the lives of those affected by it in terms of pain, quality of life, planning where the toilets are, lack of confidence eating out, etc.

The treatments are also very different. Most patients with IBS will be managed with anti-spasmodics, laxatives or Loperamide with attention to dietary and stress triggers. However patients with IBD usually require long term drug therapy ranging in potency from maintenance mesalazine to steroids and immunosuppressants to biologics such as Humira and Infliximab and even surgery.

Like all conditions there is a spectrum of severity in both IBS and IBD. Most patients are well most of the time. There is also no reason why a patient with IBD will not develop IBS – this poses a challenge for the Dr who needs to make a careful evaluation in order to avoid escalating the steroids or immunomodulators when the symptoms are in fact due to IBS. By paying attention to the patient’s history and arranging some simple investigations which include a colonoscopy, the vast majority of patients can come away from the gastroenterology clinic with a definite diagnosis.

Some useful websites to refer to for more information about these conditions include:

About the author

Dr Steven Mann MB ChB, FRCPConsultant Gastroenterologist

Dr Steven Mann has been a Consultant Gastroenterologist since 2003 with a busy NHS practice in Barnet Hospital, London (Royal Free London NHS Foundation Trust). He also consults privately at BMI Hendon, Spire Bushey Hospital, and The Kings Oak Hospital in Enfield. Dr Mann has been the Trust Lead for Clinical Nutrition, Clinical Lead for Inflammatory Bowel Diseases, and Endoscopy Training Lead. He also has a large teaching and training commitment being an Educational Supervisor and Clinical Supervisor for a number of postgraduate trainees.

In recognition of his teaching commitment he is an Honorary Senior Lecturer in the Department of Medicine at University College London. He has over 20 publications in peer reviewed journals, 30 published abstracts, and he has presented over 30 posters to national or international conferences. He is the site investigator for a number of clinical trials related to gastroenterology.

Dr Mann is happy to see and advise on any general gastroenterology problem, including indigestion, diarrhoea, constipation, irritable bowel syndrome, Crohn’s disease, colitis, bowel cancer screening. He can offer prompt consultations with access to necessary investigations such as scans in addition to endoscopy or colonoscopy which he personally does at sites local to the patient.

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The information on this site is for guidance only. It is not a substitute for professional medical care by a qualified doctor or other health care professional. Always check with your doctor if you have any concerns about your condition or treatment.